Very low temperatures are required to enable superconducting material to exhibit its properties. Power must be supplied to these superconducting devices operating at cryogenic temperatures, the power sources often at room temperature, or about 300 K. In order to drop the temperature of the power conductors or connections to the operating range of the low-temperature superconductor material (which is typically about 4K) and then maintain that temperature, supercooled gas is often used. This is because the large currents that the conductors carry generate heat due to their resistive properties. Superconductor leads must eliminate the heat generated by these large currents with thermal insulators, but instabilities and heat leaks from the material can still occur.
Since the current capacity of superconductors decreases with increasing temperature, the current capacity of the material is not enough at the high temperature end of the lead. The invention disclosed herein attempts to solve the situation, and increase current capacity, while delivering even current distribution and maximizing lead current capacity.
Uniform current distribution has been demonstrated as an important requirement in superconducting DC cables. The contact resistances where individual superconducting tapes are soldered to the copper terminals on each end create some variations as they are made or can be due to differential aging of the solder material. The variations are potential causes for non-uniform current distribution among the tapes in the cable, which adversely affects many operational parameters, such as increased AC loss, lower safety margins, and potential damage to the cable. This is the same issue as described above where the current capacity of the material is not enough at the high temperature end of the lead. Furthermore, the non-uniform current distribution is caused by the variation of contact resistance and no technical solutions have been proposed to solve this issue.
A need exists to increase current capacity of superconductors at the high temperature end of the lead. Advantageously, the configuration of superconductors will provide this increased current capacity, and maximize the total lead current capacity. Further, these developments will enable those skilled in the art to extend this methodology from magnetic resonance applications to overall HTS power cables.